In British Pat. No. 1,475,605 (J. T. de Carle) contact lenses are described which are formed from 10 to 60% of a vinyl lactam (e.g. vinyl pyrrolidone), up to 3% of a cross-linkig agent, such as ethylene glycol dimethacrylate, 0.25 to 5.6% of an unsaturated acid, such as methacrylic acid, the balance being an hydroxyalkyl acrylate or methacrylate. The resulting polymer is hydrophilic and on immersion in an aqueous alkali, carboxylate groups are formed which impart a high degree of water-absorbancy to the polymer. As a consequence the water-swollen gel-like polymers may be produced having water contents up to and above 75% by weight of the hydrated polymer and lenses manufactured from such polymers exhibit a very high atmospheric oxygen transmission rate when in hydrogel form. In fact, the permeability of the lenses to oxygen is so good that the lenses can be worn for extended periods i.e. they need not be removed after 8 hour wearing periods, which is necessary for other commercial lenses in order to satisfy the oxygen requirements of the cornea.
One problem which has been encountered with lenses manufactured in accordance with the above Patent is that they require to be handled with moderate care in order to avoid tearing the lenses when inserting or removing them.